Electric power steering apparatus

Abstract

An electric power steering apparatus according to the present invention is characterized in that a motor frame ( 20 ), a housing ( 25 ) and a plate ( 21 ) are integrally formed in such a way as to be concentric with an output axle ( 28 ) of a motor ( 11 ) and in that at least one of the motor frame ( 20 ), the housing ( 25 ), and the plate ( 21 ) is formed of magnesium or magnesium alloy.

The invention claimed is: 
     
       1. An electric power steering apparatus comprising:
 a motor frame that contains a motor; 
 a housing that contains a control circuit for controlling rotation of the motor; 
 a plate that abuts on the housing; and 
 a control apparatus frame, at least a part of which is covered by the housing, on which the control circuit and a power unit for driving the motor are mounted, and that is provided with an electrically conductive board electrically connected to the control circuit and the power unit, 
 wherein rotation of the motor is transferred to a steering axle of a vehicle by way of a transfer mechanism, 
 wherein the plate has a wall surface that extends substantially perpendicularly to a direction in which an axle center of an output axle of the motor extends, 
 wherein the control apparatus frame is arranged in such a way as to face the wall surface of the plate in the direction in which the axle center extends, 
 wherein the power unit is mounted on one surface of the control apparatus frame in such a way as to abut on the wall surface of the plate, 
 wherein the control circuit is mounted on another surface in a front and back relationship with the one surface of the control apparatus frame, 
 wherein the motor frame, the housing, and the plate are integrally formed in such a way as to be concentric with the output axle of the motor, and are juxtaposed in the direction in which the axle center extends, 
 wherein at least one of the motor frame, the housing, and the plate is formed of magnesium or magnesium alloy, 
 wherein the motor frame, the housing, and the plate are integrally fixed to one another by a screw, and 
 wherein a through hole to be penetrated by the screw is formed in at least one, of the motor frame, the housing, and the plate, that is formed of magnesium or magnesium alloy. 
 
     
     
       2. The electric power steering apparatus according to  claim 1 ,
 wherein the housing and the plate are arranged between the motor and the transfer mechanism, and 
 wherein at least one of the housing and the plate is formed of magnesium or magnesium alloy. 
 
     
     
       3. The electric power steering apparatus according to  claim 1 ,
 wherein the housing and the plate are arranged at positions, in the vicinity of the motor, that are opposite to the transfer mechanism, and 
 wherein at least one of the motor frame, the housing, and the plate is formed of magnesium or magnesium alloy. 
 
     
     
       4. The electric power steering apparatus according to  claim 1 ,
 wherein at least one of the motor frame, the housing, and the plate that is formed of magnesium or magnesium alloy is provided with a ring-shaped rib formed over almost the whole circumference thereof, 
 wherein any of the motor frame, the housing, and the plate that abuts on the at least one of the motor frame, the housing, and the plate that is formed of magnesium or magnesium alloy, is provided with a notch portion formed almost in the shape of a ring, and 
 wherein the rib and the notch portion are fixed to each other in such a way as to face each other. 
 
     
     
       5. The electric power steering apparatus according to  claim 1 ,
 wherein the housing is formed of magnesium or magnesium alloy and encloses the outer circumference of the control circuit contained therein, and 
 wherein the housing is fixed to one or both of the motor frame and the plate in such a way as to adhere thereto over almost the whole circumference thereof. 
 
     
     
       6. The electric power steering apparatus according to  claim 1 , wherein the screw is formed of a metal material having a linear-expansion coefficient almost the same as that of said at least one in which the through hole is formed.